Spatial and temporal description of the dystrophic crisis in Lesina lagoon during summer 2008

Abstract

Lagoons are vulnerable ecosystems often exposed to eutrophication due to anthropogenic activities. They are characterized by high vulnerability to climatic factors and biogeochemical impairment that, in some cases, can lead to dystrophic crisis. Here we analyze the short term temporal pattern of climatic, physical and chemical parameters during a dystrophic crisis occurred in Lesina lagoon in Summer 2008, focusing on the interactive effect of their variations. To this aim, we integrated meteorological data, satellite image analysis and local physical and chemical measurements in order to have a more detailed sight of processes that can give raise to a dystrophic crisis and to describe how the crisis evolves. Results show that an unusual change in main wind direction, sun radiation, and other meteorological parameters with respect to the previous years together with a temporal closing of tidal channel that assure the seawater inflow led to an hydrologic isolation of the western basin of Lesina lagoon occurred in summer 2008. The consequent unbalance in biogeochemical cycles produced a dystrophic crisis and a shift, in this area, from a macrophytes based system toward a phytoplankton based system. Since changes in climatic factors or in hydrologic regimes into the eutrophic lagoon probably already happened previously in different moments without giving rise to dystrophic event, the crisis was likely triggered by the co-occurrence of both factor variations. It is essential to understand the mechanistic linkages in space and time between man-made alterations of hydrologic and nutrient load regimes (that can be managed or controlled) and unpredictable climatic factors in the context of the individual ecosystem for managing transitional water ecosystems incurring in nutrient enrichment.